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authorDavid Howells <dhowells@redhat.com>2012-09-26 09:11:03 (GMT)
committerRusty Russell <rusty@rustcorp.com.au>2012-10-10 09:36:10 (GMT)
commit48ba2462ace6072741fd8d0058207d630ce93bf1 (patch)
tree3cea7661a3bd5d03631e01171c19f2123346cf01 /kernel/module_signing.c
parent631cc66eb9eaa7296e303197ff1eb0f55e32b61d (diff)
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MODSIGN: Implement module signature checking
Check the signature on the module against the keys compiled into the kernel or available in a hardware key store. Currently, only RSA keys are supported - though that's easy enough to change, and the signature is expected to contain raw components (so not a PGP or PKCS#7 formatted blob). The signature blob is expected to consist of the following pieces in order: (1) The binary identifier for the key. This is expected to match the SubjectKeyIdentifier from an X.509 certificate. Only X.509 type identifiers are currently supported. (2) The signature data, consisting of a series of MPIs in which each is in the format of a 2-byte BE word sizes followed by the content data. (3) A 12 byte information block of the form: struct module_signature { enum pkey_algo algo : 8; enum pkey_hash_algo hash : 8; enum pkey_id_type id_type : 8; u8 __pad; __be32 id_length; __be32 sig_length; }; The three enums are defined in crypto/public_key.h. 'algo' contains the public-key algorithm identifier (0->DSA, 1->RSA). 'hash' contains the digest algorithm identifier (0->MD4, 1->MD5, 2->SHA1, etc.). 'id_type' contains the public-key identifier type (0->PGP, 1->X.509). '__pad' should be 0. 'id_length' should contain in the binary identifier length in BE form. 'sig_length' should contain in the signature data length in BE form. The lengths are in BE order rather than CPU order to make dealing with cross-compilation easier. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (minor Kconfig fix)
Diffstat (limited to 'kernel/module_signing.c')
-rw-r--r--kernel/module_signing.c222
1 files changed, 221 insertions, 1 deletions
diff --git a/kernel/module_signing.c b/kernel/module_signing.c
index 499728a..6b09f69 100644
--- a/kernel/module_signing.c
+++ b/kernel/module_signing.c
@@ -11,13 +11,233 @@
#include <linux/kernel.h>
#include <linux/err.h>
+#include <crypto/public_key.h>
+#include <crypto/hash.h>
+#include <keys/asymmetric-type.h>
#include "module-internal.h"
/*
+ * Module signature information block.
+ *
+ * The constituents of the signature section are, in order:
+ *
+ * - Signer's name
+ * - Key identifier
+ * - Signature data
+ * - Information block
+ */
+struct module_signature {
+ enum pkey_algo algo : 8; /* Public-key crypto algorithm */
+ enum pkey_hash_algo hash : 8; /* Digest algorithm */
+ enum pkey_id_type id_type : 8; /* Key identifier type */
+ u8 signer_len; /* Length of signer's name */
+ u8 key_id_len; /* Length of key identifier */
+ u8 __pad[3];
+ __be32 sig_len; /* Length of signature data */
+};
+
+/*
+ * Digest the module contents.
+ */
+static struct public_key_signature *mod_make_digest(enum pkey_hash_algo hash,
+ const void *mod,
+ unsigned long modlen)
+{
+ struct public_key_signature *pks;
+ struct crypto_shash *tfm;
+ struct shash_desc *desc;
+ size_t digest_size, desc_size;
+ int ret;
+
+ pr_devel("==>%s()\n", __func__);
+
+ /* Allocate the hashing algorithm we're going to need and find out how
+ * big the hash operational data will be.
+ */
+ tfm = crypto_alloc_shash(pkey_hash_algo[hash], 0, 0);
+ if (IS_ERR(tfm))
+ return (PTR_ERR(tfm) == -ENOENT) ? ERR_PTR(-ENOPKG) : ERR_CAST(tfm);
+
+ desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
+ digest_size = crypto_shash_digestsize(tfm);
+
+ /* We allocate the hash operational data storage on the end of our
+ * context data and the digest output buffer on the end of that.
+ */
+ ret = -ENOMEM;
+ pks = kzalloc(digest_size + sizeof(*pks) + desc_size, GFP_KERNEL);
+ if (!pks)
+ goto error_no_pks;
+
+ pks->pkey_hash_algo = hash;
+ pks->digest = (u8 *)pks + sizeof(*pks) + desc_size;
+ pks->digest_size = digest_size;
+
+ desc = (void *)pks + sizeof(*pks);
+ desc->tfm = tfm;
+ desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+
+ ret = crypto_shash_init(desc);
+ if (ret < 0)
+ goto error;
+
+ ret = crypto_shash_finup(desc, mod, modlen, pks->digest);
+ if (ret < 0)
+ goto error;
+
+ crypto_free_shash(tfm);
+ pr_devel("<==%s() = ok\n", __func__);
+ return pks;
+
+error:
+ kfree(pks);
+error_no_pks:
+ crypto_free_shash(tfm);
+ pr_devel("<==%s() = %d\n", __func__, ret);
+ return ERR_PTR(ret);
+}
+
+/*
+ * Extract an MPI array from the signature data. This represents the actual
+ * signature. Each raw MPI is prefaced by a BE 2-byte value indicating the
+ * size of the MPI in bytes.
+ *
+ * RSA signatures only have one MPI, so currently we only read one.
+ */
+static int mod_extract_mpi_array(struct public_key_signature *pks,
+ const void *data, size_t len)
+{
+ size_t nbytes;
+ MPI mpi;
+
+ if (len < 3)
+ return -EBADMSG;
+ nbytes = ((const u8 *)data)[0] << 8 | ((const u8 *)data)[1];
+ data += 2;
+ len -= 2;
+ if (len != nbytes)
+ return -EBADMSG;
+
+ mpi = mpi_read_raw_data(data, nbytes);
+ if (!mpi)
+ return -ENOMEM;
+ pks->mpi[0] = mpi;
+ pks->nr_mpi = 1;
+ return 0;
+}
+
+/*
+ * Request an asymmetric key.
+ */
+static struct key *request_asymmetric_key(const char *signer, size_t signer_len,
+ const u8 *key_id, size_t key_id_len)
+{
+ key_ref_t key;
+ size_t i;
+ char *id, *q;
+
+ pr_devel("==>%s(,%zu,,%zu)\n", __func__, signer_len, key_id_len);
+
+ /* Construct an identifier. */
+ id = kmalloc(signer_len + 2 + key_id_len * 2 + 1, GFP_KERNEL);
+ if (!id)
+ return ERR_PTR(-ENOKEY);
+
+ memcpy(id, signer, signer_len);
+
+ q = id + signer_len;
+ *q++ = ':';
+ *q++ = ' ';
+ for (i = 0; i < key_id_len; i++) {
+ *q++ = hex_asc[*key_id >> 4];
+ *q++ = hex_asc[*key_id++ & 0x0f];
+ }
+
+ *q = 0;
+
+ pr_debug("Look up: \"%s\"\n", id);
+
+ key = keyring_search(make_key_ref(modsign_keyring, 1),
+ &key_type_asymmetric, id);
+ if (IS_ERR(key))
+ pr_warn("Request for unknown module key '%s' err %ld\n",
+ id, PTR_ERR(key));
+ kfree(id);
+
+ if (IS_ERR(key)) {
+ switch (PTR_ERR(key)) {
+ /* Hide some search errors */
+ case -EACCES:
+ case -ENOTDIR:
+ case -EAGAIN:
+ return ERR_PTR(-ENOKEY);
+ default:
+ return ERR_CAST(key);
+ }
+ }
+
+ pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key_ref_to_ptr(key)));
+ return key_ref_to_ptr(key);
+}
+
+/*
* Verify the signature on a module.
*/
int mod_verify_sig(const void *mod, unsigned long modlen,
const void *sig, unsigned long siglen)
{
- return -ENOKEY;
+ struct public_key_signature *pks;
+ struct module_signature ms;
+ struct key *key;
+ size_t sig_len;
+ int ret;
+
+ pr_devel("==>%s(,%lu,,%lu,)\n", __func__, modlen, siglen);
+
+ if (siglen <= sizeof(ms))
+ return -EBADMSG;
+
+ memcpy(&ms, sig + (siglen - sizeof(ms)), sizeof(ms));
+ siglen -= sizeof(ms);
+
+ sig_len = be32_to_cpu(ms.sig_len);
+ if (sig_len >= siglen ||
+ siglen - sig_len != (size_t)ms.signer_len + ms.key_id_len)
+ return -EBADMSG;
+
+ /* For the moment, only support RSA and X.509 identifiers */
+ if (ms.algo != PKEY_ALGO_RSA ||
+ ms.id_type != PKEY_ID_X509)
+ return -ENOPKG;
+
+ if (ms.hash >= PKEY_HASH__LAST ||
+ !pkey_hash_algo[ms.hash])
+ return -ENOPKG;
+
+ key = request_asymmetric_key(sig, ms.signer_len,
+ sig + ms.signer_len, ms.key_id_len);
+ if (IS_ERR(key))
+ return PTR_ERR(key);
+
+ pks = mod_make_digest(ms.hash, mod, modlen);
+ if (IS_ERR(pks)) {
+ ret = PTR_ERR(pks);
+ goto error_put_key;
+ }
+
+ ret = mod_extract_mpi_array(pks, sig + ms.signer_len + ms.key_id_len,
+ sig_len);
+ if (ret < 0)
+ goto error_free_pks;
+
+ ret = verify_signature(key, pks);
+ pr_devel("verify_signature() = %d\n", ret);
+
+error_free_pks:
+ mpi_free(pks->rsa.s);
+ kfree(pks);
+error_put_key:
+ key_put(key);
+ pr_devel("<==%s() = %d\n", __func__, ret);
+ return ret;
}